1. Field of the Invention
The present invention relates to a novel surface coatings in which the binder is a two-component system containing a polyisocyanate component and a specific component containing isocyanate-reactive groups, and to their use for the production of coatings on any desired substrate.
2. Description of the Prior Art
Two-component coating compositions that contain as binding agent a polyisocyanate component in combination with an isocyanate-reactive component, especially a polyhydroxyl component, are known. They are suitable for the production of high-grade surface coatings that can be adjusted to be hard, resilient, abrasion- and solvent-resistant and, above all, also weather resistant.
In accordance with the present invention novel two-component coating compositions are used in which the binding agent is based on a two-component system containing a polyisocyanate component and an isocyanate-reactive component, which is composed entirely or partly of a mixture of specific secondary polyamines and oxazolidines described in more detail hereinafter.
The secondary polyamines are polyaspartic acid esters such as those described in EP-A-0,403,921. These secondary amines, in combination with polyisocyanates, are especially suited as binding agents in coating compositions containing few or no solvents and allow the coatings to be cured rapidly at low temperatures.
The use of oxazolidines with polyisocyanates as moisture-hardening reactive systems for coatings, adhesives and other applications is also known and is described, for example, in U.S. Pat. Nos. 3,661,923, 3,743,626, 3,912,691, 4,024,117, 4,032,686, 4,101,527, 4,118,376, 4,138,545 and 4,471,102.
In EP-A-0,531,249, novel coating compositions that dry at ambient temperature are described. These compositions contain mixtures of hydroxy-functional resins with isocyanates and aldimines or ketimines. The compositions may also contain reactive diluents consisting of secondary amines, alcohols or oxazolidines.
It is known, however, that coating formulations that contain ketimines or aldimines turn yellow to a marked extent both in the form of the liquid coating composition and in cured form and, thus, are consequently less suitable for finishing coatings of the highest quality. The same applies also to coating formulations that contain ketimines or aldimines and polyaspartic acid esters.
Although coating systems with oxazolidines exhibit similar yellowing phenomena, it has surprisingly been found that, even after drying at low temperatures, surface coatings having outstanding properties, especially a lesser tendency to turn yellow and very good resistance to solvents, can be obtained when they are produced using two-component coating compositions in which the binder is based on a polyisocyanate component and an isocyanate-reactive component containing entirely or partly a mixture of polyaspartic acid esters and oxazolidines.